A single amino acid substitution (Glu134--&gt;Ala) in NhaR1 increases the inducibility by Na+ of the product of nhaA, a Na+/H+ antiporter gene in Escherichia coli.

Carmel, O.; Dover, Nir; Rahav‐Manor, O.; Dibrov, Pavel; Kirsch, Donald R.; Karpel, R; Schuldiner, Shimon; Padan, Etana

doi:10.1002/j.1460-2075.1994.tb06467.x

Cited by 20 publications

(16 citation statements)

References 36 publications

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“…The expression of this antiporter is specifically induced by Na + and Li + and requires NhaR, a positive regulator that belongs to the OxyR-LysR family of transcription factors [20]. Mutations in this regulatory gone have been isolated that affect the Na + sensitivity of nhaA expression, suggesting that NhaR might represent a Na + sensor [21].…”

Section: ~ Discussionmentioning

confidence: 99%

Multiple transduction pathways regulate the sodium‐extrusion gene PMR2/ENA1 during salt stress in yeast

1996

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The yeast PMR21£NAI gene encodes an ATPase involved in sodium extrusion and induced by NaCI. At low salt concentrations (0.3 1VID induction is mediated by the HOG-MAP kinase pathway, a system activated by non-specific osmotic stre&~. At high salt concentrations (0.8 M) induction i~ mediated by the protein phosphatase caleineurin and is specific for sodium. Protein kinase A and Sis2ptHal3p modulate PMR21£NAI expression as negative and positive factors, respectively but Sis2p/Hal3p does not perticipate in the transduction of the salt signal. Salt stress dect'eases the level of cAMP and the resulting decrease in protein kinase A activity may contribute t6 HOGmediated Induction.Key words: Signal transduction; Salt stress; MAP kinase; Calcineurin; cAMP; Saccharomyces cerevisiae 1. Introductit, n Living cells can withstand a variety of stress conditions such as extreme temperatures, water deficit, high salt concentrations, starvation etc. Under these circumstances organisms modify their cellular machinery in order to counteract the deleterious effect of damaging agents. This constitutes a stress response and involves modulation of enzymatic activities as well as changes in gene expression [1,2]. In ~'ecent years considerable interest has been raised by the mechanisms of plant tolerance to drought and salinity, two major factors limiting agricultural productivity [3]. The signal transduction pathways operating during osmotic and salt stress are only partially understood and this gap of knowledge is a limiting factor for urgent biotechnological applications [2].The yeast Saccharomyces cerevisiae can be utilized as a convenient model system in salinity studies [2]. Salt stress has two major harmful effects for cells: the loss of turgor pressure and the toxicity of Na ÷ ions to cellular metabolism. The adaptation of yeast to these conditions requires the modification of the plasma membrane transport systems to exclude Na + ions from the cytosol and the onset of glycerol synthesis to restore turgor pressure. This adaptation is largely based on changes in the expression of key genes such as PMR21ENAI (in the following referred to as ENAI), encoding an ATPase involved in sodium extrusion [4], and GPDI, encoding~a dehydrogenase involved in gljcerol synthesis [5]. Many other genes are also induced by saP, stress whose contribution to the adaptatio,a, if any, is not well understood [2].In the present work we have investigated the environmental signals and tran,,~lucing pathways mediating the induction of *Corresponding author'. Fax: (34) (6) Materials and methodsYPD and synthetic medium were prepared as described [12]. YPD contained 2% glucose, 1% yeast extract and 2% peptone. Synthetic medium contained 2% glucose, 0.7% yeast nitrogen base without amino acids (Difco), 50 mM MES [2.(N-morpholino) ethanosulfonic acid] adjusted to pH 6.0 with Tris and the amino acids, purine and pyrimidine bases required by the strains.Strains YPH499 (MATs ura3 leu2 his3 trpl lys2 ado2) and JBY10 (isogonic to YPH499 with hogl.Al:: TRPI) ...

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Section: ~ Discussionmentioning

confidence: 99%

Multiple transduction pathways regulate the sodium‐extrusion gene PMR2/ENA1 during salt stress in yeast

1996

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“…The E. coil nhaA gene encoding a sodiumproton antiporter is positively regulated by nhaR, which encodes a protein belonging to the LysR family of transcriptional regulators . The NhaR protein may function as a sensor of the intracellular Na ÷ concentration (Carmel et al, 1994). The Na ÷ requirement for the expression of the citrate-specific fermentation genes is plausible, since three enzymes involved in citrate metabolism are dependent on this alkali metal ion (Fig.…”

Section: Discussionmentioning

confidence: 99%

Regulation of anaerobic citrate metabolism in Klebsiella pneumoniae

Bott

Meyer

Dimroth

1995

Molecular Microbiology

128

167

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Three enzymes are specifically required for uptake and catabolism of citrate by Klebsiella pneumoniae under anaerobic conditions: a Na+ -dependent citrate carrier (CitS), citrate lyase (CitDEF), and the Na+ pump oxaloacetate decarboxylase (OadGAB). The corresponding genes are clustered on the chromosome, with the citCDEFG genes located upstream and divergent to the citS-oadGAB genes. We found that expression of citS from its native promoter in Escherichia coli requires the DNA region downstream of oadB. Nucleotide sequence analysis of this region revealed the presence of two adjacent genes, citA and citB. By sequence similarity, the predicted CitA and CitB proteins were identified as members of the two-component regulatory systems. The sensor kinase CitA contained, in the N-terminal half, two putative transmembrane helices which enclosed a presumably periplasmic domain of about 130 amino acids. The C-terminal half of the response regulator CitB harboured a helix-turn-helix motif typical of DNA-binding proteins. K. pneumoniae citB null mutants were unable to grow anaerobically with citrate as the sole carbon and energy source (Cit- phenotype). When cultivated anaerobically with citrate plus glycerol, all of the citrate-specific fermentation enzymes were synthesized in the wild type, but not in the citB mutants. This showed that citS, oadGAB and citDEF required the CitB protein for expression and therefore are part of a regulon. In the wild type, synthesis of CitS, oxaloacetate decarboxylase and citrate lyase was dependent on the presence of citrate, sodium ions and a low oxygen tension. In a citA null mutant which expressed citB constitutively at high levels, none of these signals was required for the formation of the citrate fermentation enzymes. This result suggested that citrate, Na+, and oxygen exerted their regulatory effects via the CitA/CitB system. In the presence of these signals, the citAB gene products induced their own synthesis. The positive autoregulation occurred via co-transcription of citAB with citS and oadGAB.

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“…The absolute requirement for Na + for pH homeostasis in alkaliphilic bacteria and diminished Na + /H + antiporter activity in nonalkaliphilic mutants then provided strong support for an antiporter based pH homeostasis mechanism [39,87,88]. Study of a Li + resistant mutant [89] led to the first cloning of an antiporter gene, Ec-nhaA of E. coli [90,91] and its regulator Ec-nhaR [92]. Ec-NhaA is the main antiporter of E. coli and many enterobacteria [37].…”

Section: Identification Of Genes/proteins Involved In Alkaline Ph Hommentioning

confidence: 99%

Alkaline pH homeostasis in bacteria: New insights

Padan

Bibi

Ito

et al. 2005

Biochimica et Biophysica Acta (BBA) - Biomembranes

672

633

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The capacity of bacteria to survive and grow at alkaline pH values is of widespread importance in the epidemiology of pathogenic bacteria, in remediation and industrial settings, as well as in marine, plant-associated and extremely alkaline ecological niches. Alkali-tolerance and alkaliphily, in turn, strongly depend upon mechanisms for alkaline pH homeostasis, as shown in pH shift experiments and growth experiments in chemostats at different external pH values. Transcriptome and proteome analyses have recently complemented physiological and genetic studies, revealing numerous adaptations that contribute to alkaline pH homeostasis. These include elevated levels of transporters and enzymes that promote proton capture and retention (e.g., the ATP synthase and monovalent cation/proton antiporters), metabolic changes that lead to increased acid production, and changes in the cell surface layers that contribute to cytoplasmic proton retention. Targeted studies over the past decade have followed up the long-recognized importance of monovalent cations in active pH homeostasis. These studies show the centrality of monovalent cation/proton antiporters in this process while microbial genomics provides information about the constellation of such antiporters in individual strains. A comprehensive phylogenetic analysis of both eukaryotic and prokaryotic genome databases has identified orthologs from bacteria to humans that allow better understanding of the specific functions and physiological roles of the antiporters. Detailed information about the properties of multiple antiporters in individual strains is starting to explain how specific monovalent cation/proton antiporters play dominant roles in alkaline pH homeostasis in cells that have several additional antiporters catalyzing ostensibly similar reactions. New insights into the pH-dependent Na(+)/H(+) antiporter NhaA that plays an important role in Escherichia coli have recently emerged from the determination of the structure of NhaA. This review highlights the approaches, major findings and unresolved problems in alkaline pH homeostasis, focusing on the small number of well-characterized alkali-tolerant and extremely alkaliphilic bacteria.

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A single amino acid substitution (Glu134-->Ala) in NhaR1 increases the inducibility by Na+ of the product of nhaA, a Na+/H+ antiporter gene in Escherichia coli.

Cited by 20 publications

References 36 publications

Multiple transduction pathways regulate the sodium‐extrusion gene PMR2/ENA1 during salt stress in yeast

Multiple transduction pathways regulate the sodium‐extrusion gene PMR2/ENA1 during salt stress in yeast

Regulation of anaerobic citrate metabolism in Klebsiella pneumoniae

Alkaline pH homeostasis in bacteria: New insights

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